hydro foil

[Ken6645]

I found an old stingray hydro foil that I installed on a 1994 Evinrude 90 GT to get me on plane quicker..Worked great. Just fooling around last night I installed it on my 1969- 18 hp Evinrude .My question is will this "foil" have any adverse effects on my little 18 hp motor ? like overheating . I think I read somewhere that foils change the cavatations [sp] and could cause overheating? I would hate to burn up a good motors. if anyone has a pro or con opinion ,I would appreciate a heads-up...
thanks for your time
Ken

 

[ondarvr]

Re: hydro foil

Overheating wouldn't be an issue from just bolting one on...but what are you trying to achieve by using it?

The purpose of a foil is to allow you to raise the motor higher which "may" result in better performance.

 

[Ken6645]

Re: hydro foil

to begin, I had a long shaft motor on a short tramson . No plane just straight up..Got a jackplate and achieved a 5 inch height distance
and a 4 inch setback distance. According to several friends this is what I needed.Now with the changes this brings the water intake really close to the surface.I know that the foil will flatten the water behind the motor.Thats my concern .I suppose I should try it without foil first .just thinking that the foil might give me to much lift.
ken

Overheating wouldn't be an issue from just bolting one on...but what are you trying to achieve by using it?

The purpose of a foil is to allow you to raise the motor higher which "may" result in better performance.

 

[steelespike]

Re: hydro foil

The purpose of the foil is to lift the stern to get the boat out of the hole. Also if your lucky it may reduce bow height some
and dampen the bow bounding around.
It can also cause strange handling,too much hull in the water and reduce speed.
Give it a try. Let us know what you find. There are a couple of things we couldd check that may help you more than the foil..
Let us know about your setup;boat,motor prop size(probably 9 1/4 X 11).
On a light reasonably fast boat a 18 is rated for about 27 mph. If you get a Tinytach $47 and a gps we could play around with your setup

 

[steelespike]

Re: hydro foil

definitely should try without the foil first till you have the motor height just right.
The jack plate will require the motor to be a little higher as the water farther behind is slightly higher than near the transom .
The water is also slightly cleaner( less roiled).

 

[ondarvr]

Re: hydro foil

The purpose of the foil is to lift the stern to get the boat out of the hole. Also if your lucky it may reduce bow height some
and dampen the bow bounding around.
It can also cause strange handling,too much hull in the water and reduce speed.

This is not really what a foil is designed to do, only how they get used by many people. This is what creates all the negative affects that may come by not doing the proper set up and adjusting it correctly. The positve results are only a possibility, not all setups can use a foil.

 

[ondarvr]

Re: hydro foil

to begin, I had a long shaft motor on a short tramson . No plane just straight up..Got a jackplate and achieved a 5 inch height distance
and a 4 inch setback distance. According to several friends this is what I needed.Now with the changes this brings the water intake really close to the surface.I know that the foil will flatten the water behind the motor.Thats my concern .I suppose I should try it without foil first .just thinking that the foil might give me to much lift.
ken

A foil’s function is to allow you raise the motor higher without the prop sucking water from the surface (Ventilating), it should not be dragging in the water and shouldn’t have an affect on the cooling water entering the motor. That is unless you raise the motor too high. Raising the motor “may” increase performance.

The AV plate on your motor may be different than most more current motors though, I’m not sure when they changed them on that model, if they ever did.

 

[sutor623]

Re: hydro foil

This is not really what a foil is designed to do, only how they get used by many people. This is what creates all the negative affects that may come by not doing the proper set up and adjusting it correctly. The positve results are only a possibility, not all setups can use a foil.

definitely should try without the foil first till you have the motor height just right.

I'd pick my battles wisely. Steele has never given me bad advice. He is the Prop goto guy on here. And Steele is clearly discouraging the OP from just bolting a foil on with high hopes.

 

[steelespike]

Re: hydro foil

A foil’s function is to allow you raise the motor higher without the prop sucking water from the surface (Ventilating), it should not be dragging in the water and shouldn’t have an affect on the cooling water entering the motor. That is unless you raise the motor too high. Raising the motor “may” increase performance.

The AV plate on your motor may be different than most more current motors though, I’m not sure when they changed them on that model, if the ever did.

The Whale Tale and Doelfin are specifically to improve hole shot and ability to stay on plane any affect on ventilation(cavitation)
is coincidental. their affect does depend on the motor set up and they do need to be near or at the surface.Or can create lots a of unwanted results including loss of speed.

 

[ondarvr]

Re: hydro foil

I'd pick my battles wisely. Steele has never given me bad advice. He is the Prop goto guy on here. And Steele is clearly discouraging the OP from just bolting a foil on with high hopes.

No argument with steel, only relating facts to the OP about foils and how they are to be used correctly. Foils are so misunderstood that many people ask the same questions thinking a foil and tabs do the same thing, and they don't. Tabs are what 90% of the people need, foils "may" be of some value, but they aren't a bolt it on and head to the water with great expectations type of tool. It takes some work to make them function correctly and only "if" boat setup can be helped with one. Tabs weren’t mentioned in the question by the OP, but they are so frequently compared I thought I would throw it in.

In this case if the motor is mounted high due to the jack plate and set back, then a foil may be of some value in keeping the prop from ventilating. But as Steel said, he should run it without the foil to see if there is even a problem that needs attention.

 

[steelespike]

Re: hydro foil

Here is the description of the DoelFin performance features.Greater stability,consistent planing at lower rpm,faster out of the hole,steadier turns,higher top end speeds,lower bow rise at all speeds.

 

[ondarvr]

Re: hydro foil

The Whale Tale and Doelfin are specifically to improve hole shot and ability to stay on plane any affect on ventilation(cavitation)
is coincidental. their affect does depend on the motor set up and they do need to be near or at the surface.Or can create lots a of unwanted results including loss of speed.

The advertising on the package lists these things, and when used incorrectly they can have an effect in this area, that's not what they actually do though. Used in this way they are of little value and may create problems, tabs are much better.

When used correctly you are not relying on the foil dragging in the water, only its ability to prevent ventilation so you can raise the motor.

They have little or no effect on cavitation, only ventilation.

 

[steelespike]

Re: hydro foil

I only included "cavitation' with Ventilation for those not acquainted with modern day terminology.
cavitation was used to describe ventilation even by Outboard companies years ago.
The things I listed are from the Techical information paragraph. On the site I looked up.
"foil" describes A shape that lifts. "Airfoil" on air planes "Hydrofoil" on boats.
There are Hydrofoils that lift boats completely out of the water.
So Are you saying "Hydrofoils" don't work except to control venting? Or "Hydrofoils" were created to control venting?
HydroFloils Do as they are described We had" Doelfins"On my mothers 15' 50 hp outboard and My sisters 18' 3.0.Cobia.
These did exactly as they advertised.Though I have no data on the actual speed increase if any.

 

[ondarvr]

Re: hydro foil

back to this.

The result of using a foil and raising the motor can be better a hole shot and faster planing. This is because as you raise the motor it has less leverage on the hull, resulting in less bow rise. You will also have less ventilation, so instead of the prop being surrounded by a mix of air and water, it’s only water, for a much better bite. The foil just stops the prop from sucking air from the surface. (This is really its only function.)

Lower planning speed from less bow rise is from less leverage. This is also an area where the foil dragging in the water will (may) supply some lift too, but this is a side affect. If you need the foil dragging in the water to make improvements you want, then you don’t need a foil, you need tabs.

Less Porpoising is for the same reason, less bow lift because of less leverage. The foil shouldn’t be in the water now though.

Better top speed and MPG. This is from the motor being higher and having less gear case in the water, resulting in less drag. Should be good for a couple of hundred RPM.

The problem with foils is that they really can only be fine tuned when used on an outboard, and then only if the setup can make use of one. On an I/O you can only bolt it on and hope for the best. If it helps in few areas and the possible negative side affects can be lived with, then it may work OK for you. Most buyers just pull it out of the package and bolt it on with none of the other work involved to set it up correctly. This results in all the negative comments and opinions out there.

The best set up is a hydraulic jack plate and a good selection of stainless props. This way it can be set for the best holeshot, low speed planing, then fine tuned for the best speed and handling with the current load and water conditions.

 

[ondarvr]

Re: hydro foil

I only included "cavitation' with Ventilation for those not acquainted with modern day terminology.
cavitation was used to describe ventilation even by Outboard companies years ago.
The things I listed are from the Techical information paragraph. On the site I looked up.
"foil" describes A shape that lifts. "Airfoil" on air planes "Hydrofoil" on boats.
There are Hydrofoils that lift boats completely out of the water.
So Are you saying "Hydrofoils" don't work except to control venting? Or "Hydrofoils" were created to control venting?
HydroFloils Do as they are described We had" Doelfins"On my mothers 15' 50 hp outboard and My sisters 18' 3.0.Cobia.
These did exactly as they advertised.Though I have no data on the actual speed increase if any.

The term foil in this case is more of a marketing term that evolved into the shape of most plastic “enlarged AV plates”, which is all a foil or fin is. A flat plate will do the same thing, but there is no way for a company to make money if all people did was steal street signs and cut them to fit. They need to make these things look sexy, so they create different shapes and designs. I would think some work better than others, but their performance may change depending on the exact set up and whether it’s an I/O or outboard.

A true hydrofoil (as you mentioned) is used for lift and the hydrodynamics are critical to its performance.